Project 3, The 1918 HA and NA: Antigens and Virulence Factors, seeks to use a combination of reverse genetics, molecular biological, biochemical and serological assays to further our understanding of the contributions at the molecular level, of the HA and NA proteins of the 1918 virus in virulence, and to assess the antigenic novelty of the 1918 surface glycoproteins. Preliminary data suggest that the 1918 HA and NA confer a high virulence phenotype upon influenza viruses in mice Tumpey, et al. (2002) PNAS 99, 13849-54. This project will evaluate the hypothesis that the high mortality rate of the 1918 pandemic was influenced both by the existence of an immunologically naive human population and by additional properties of the 1918 virus HA and NA. Pathogenesis studies of recombinant viruses containing 1918 HA and NA genes will be conducted in mice and chickens and will further evaluate the role of these proteins in virulence. In addition, Dr. Basler's laboratory will be reconstructing genes of the 1918 genes according to the sequences generated by Dr. Taubenberger. These reconstructed genes will be used by the different projects of the program project.